1. Field of the Invention
The present invention relates to a rotation detecting device for detecting a rotation angle of a rotator that is a subject of detection, such as a vehicular steering shaft.
2. Description of the Related Art
FIG. 8 is a schematic view showing a structure of a conventional electrically-operated power steering control device (hereinafter, referred to as EPS control device) and a rotation detecting device for detecting a rotation angle of a steering shaft.
As shown in FIG. 8, the steering shaft 2 fixed in a center of a steering wheel 1 is rotatably held by a support member 6 provided in a dashboard of a vehicular compartment. The steering shaft 2 has a tip integrally provided or fixed with a detecting shaft part 3, at a tip of which a steering output part 4 is further provided. The steering output part 4 has a tip coupled with a manual steering gear. Front-wheel tires are secured on the wheels provided at the both ends of the manual steering gear.
The steering output part 4 is fixed with a worm wheel 5 as a power assist rotator. In the vicinity of the worm wheel 5, an electrically-operated power assist motor 7 is provided. The power assist motor 7 has an output shaft 7a fixed with a worm gear 8. The worm gear 8 is in mesh with the teeth 5a in the outer periphery of the worm wheel 5.
The detecting shaft part 3 is provided with a torque detecting device 9 and a rotation detecting device 10. In the torque detecting device 9, the torque applied to the detecting shaft part 3 is converted into a voltage or the like, an output of which is provided to a torque-detection control section of a microcomputer or the like. In the torque-detection control section, an assist amount is operated on the basis of the torque output and a vehicle-speed signal, ignition-on signal or the like. On the basis of the operation value, the power assist motor 7 is placed under control. The power of the power assist motor 7 is provided to the steering shaft 2, to thereby set a steering force of the steering wheel 1.
Meanwhile, the rotation detecting device 10 is for detecting a rotation angle of the steering shaft 2. For example, in the case over-steering or under-steering takes place on the vehicle during driving, an optimal steering angle is indexed, by the microcomputer, from the steering angle detected by the rotation detecting device 10, the vehicle speed and the like. The power assist motor 7 is placed under control, to adjust the steering angle of the front wheels or regulate the brake force, thereby steering the automobile in the optimal state.
However, the conventional rotation detecting device 10 is constructed with the detecting shaft part 3 of the steering shaft inserted through a central part thereof. Within the rotation detecting device 10, there are provided a rotating part fitted on an outer periphery of the detecting shaft part 3 and rotating in unison with the detecting shaft part 3, and a detection rotating member to be operated by the rotating part, whereby a rotation angle of the detecting rotating member can be detected by a detecting element. In this manner, the rotation detecting device 10 is constructed by arranging the detection rotating member and the detecting element in the outer peripheral region of the steering shaft 2. Consequently, the rotation detecting device 10 has an increased size of outer diameter.
Meanwhile, the rotation detecting device 10 is required to linearly detect a rotation angle of less than 360 degrees of the steering shaft 2. Accordingly, basically, it is preferred to provide a detection rotating member rotatable with a correspondence of 1:1 to the rotation angle of the steering shaft, thereby detecting a rotation angle of the rotating member. However, in order to set a rotation angle ratio of 1:1, there is a need to arrange a gear having the same diameter as the rotation part fitted on the outer periphery of the detection shaft part 3. Therefore, the rotation detecting device 10 is size-increased furthermore.
However, because of the difficulty in securing a space for arranging a large-sized rotation detecting device 10 around the steering shaft 2, the conventional rotation detecting device 10 is arranged therein with a gear having a small diameter. As a result, the rotation of the steering shaft 2 is speed-increased and conveyed to the detection rotation member, e.g. the detection rotating member rotates twice or trice during once rotation of the steering shaft 2. Consequently, in order to correctly detect a rotation angle of the steering shaft 2, there is a necessity to newly provide detecting means that generates a pulse whenever the detection rotating member rotates once, for example. Namely, unless the detecting means is provided, the same signals would be outputted twice or trice from the detecting element detecting a rotation angle of the detection rotating member before the steering shalt 2 rotates 360 degrees, resulting in the impossibility to correctly detect a steering angle.
It is an object of the present invention to provide a rotation detecting device which can be made in a small-sized structure and moreover have a rotation angle ratio of a subject-of-detection and detection rotation member placed in a correspondence of 1:1.
It is another object of the invention to provide a rotation detecting device having a space around the steering shaft allowed for effective utilization.